The invention relates to steering systems for multitrack wheeled vehicles.
This application claims the priority of German patent application 196 05 553.9, the disclosure of which is expressly incorporated by reference herein.
In conventional steering systems for road vehicles, a steering wheel is positively coupled to the steered vehicle wheels by a mechanical transmission. However, steering systems without mechanical positive coupling of this kind between the steering member and the steered vehicle wheels are now being designed. In relatively simple systems, for example, hydraulic positive coupling is provided between the steering member and the steered vehicle wheels. Moreover, systems are also being developed which are intended to dispense with all positive coupling between the steering member and the steered vehicle wheels. Instead, the steering member actuates a desired-value transmitter which is provided as part of an electronic control path that controls a servo motor. The servo motor actuates the steered vehicle wheels in accordance with a desired value/actual value comparison, and also controls a hand-force adjuster which sets a predeterminable reaction force, generally dependent on the driving state, at the steering member. In this manner, it is possible to control virtually any steering behavior, and in special driving situations it is possible to perform autonomous steering interventions as a function of parameters which are to be evaluated.
In principle, systems of this kind can be designed to be very reliable. Similar systems are already in use, for example, for the actuation of control surfaces on aircraft, the term "fly by wire" having passed into common usage. The reliability of such systems is ensured by multiple redundancy.
It is the object of the present invention to provide an advantageous arrangement for redundancy in such steering systems for vehicles.
This object is achieved according to the invention by providing, in addition to a main steering system that controls the steered vehicle wheels by changing the steering angle, an emergency steering system which can be switched on (or automatically switches itself on) if the main steering system fails, and which controls the steering of the vehicle by actuating wheel brakes on different sides of the vehicle unequally as a function of the actuation of a steering member. The invention is based on the general idea of using electronically controlled brake systems, which are known in principle (and which permit independent control of the braking forces on each wheel to avoid lock-up during braking), to give controllably different distribution of the braking forces between wheels on different sides of the vehicle in order still to permit steering maneuvers, for example a lane change, in emergencies.
In a preferred embodiment of the invention, the steered vehicle wheels have a sufficient steering offset so that it is also possible, by correspondingly different control of the wheel brakes of these wheels, to achieve a change in the steering angle and hence "conventional" steering of these wheels.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.